When you get right down to it, deadheading is a gardenerís means of fooling Mother Nature!
If left to its own desires, a flowering plant would put forth a bloom, the blossom would be fertilized, and the ripening ovary would become a fruit. If the task of reproduction was completed, the plant would expend its energy and nutrients to the developing fruit instead of the production of more flowers.
Deadheading, the removal of spent blossoms with the aim of forcing a plant to rebloom, is our technique for tricking the plant into thinking it has failed in this reproductive process. By removing the blossom before it has had a chance to fully develop a fruit, the plant sends out regrowth hormones, produces a new bloom, and tries again.
Traditionally, rosarians have defined deadheading as the careful removal of the bloom stem down to the first or second, five leaf set (sometimes called a true leaf). I suggest this may not always be the best procedure.
Deadheading remontant (repeat-blooming) roses has multiple functions. Not only will it conserve plant energy and produce more blooms, it will also remove hiding places and food for insects which often become pests in our garden. It may even permit minor improvements in air circulation, thus reducing the potential for fungal diseases.
Learning to deadhead properly is essential to good rose production. So how do we do that?
Two important tips to remember: Barring genetic mutations and certain viral diseases, a bloom stem can be no larger in diameter than the stem from which it grows. Furthermore, the subsequent blooms will be proportionate in size to the stem from which they emerge. This means the further down the stem you cut, the larger the bloom stem and subsequent buds will become, and hence, the longer it will take for the rose to rebloom.
All cuts are best made at an angle away from and slightly above the node. (If cane boring mini-wasps are a problem, you may wish to seal the cut with white glue or a tiny drop of orange shellac. Otherwise, the plant should seal its own cut within a few minutes.) Stem growth will begin from the nodes nearest to the cut. Therefore, the subsequent bloom stem will be slightly smaller than the stem you have just removed. And deciding how far down the stem to make that cut is best determined by using good judgment.
If your rose produces a cluster of blooms, you may want to deadhead further back on the stem. If, however, you are growing a Hybrid Tea and religiously disbud, then deadheading further down the stem should be tempered with how large you expect the second bloom to become and how soon you want the rose to recycle.
So far, we have only talked about modern roses and their close relatives. Many antique and Old Garden roses bloom in clusters from multiple nodes near the terminus of the cane. In this case, trimming the spent clusters rather than finding the true leaf should be your focus. The secondary clusters, those blooming below the terminal cluster, will still be blooming when the primary cluster has finished. After all the clusters have finished blooming, the stem can be trimmed further down, but regrowth will require a bit more time to produce a second flush.
For obvious reasons, deadheading to promote more bloom only works on plants that have the capability to rebloom.
Many of our roses do not have the capability to rebloom. If hips are not desired, then deadheading may be an
option to reduce infestation of insects that prefer decaying plant material. Critters particularly fond of spent
roses and their fallen petals include earwigs, sow and pill bugs, and cucumber beetles. Similarly, thrips can find
a home in spent blossoms.
By Mark Whitelaw, Kindly Provided by Laura Whitelaw